mash: Remove StatusAreaWidget references from system tray classes

ash/system/chromeos/session/logout_button_tray.h

Index: ash/system/chromeos/session/logout_button_tray.h
diff --git a/ash/system/chromeos/session/logout_button_tray.h b/ash/system/chromeos/session/logout_button_tray.h
index 29fcb74343fe7f57815a258c60bc4994627a420e..58bd8e05e1a052b4725582e51fc6ccae9a9b7e99 100644
--- a/ash/system/chromeos/session/logout_button_tray.h
+++ b/ash/system/chromeos/session/logout_button_tray.h
@@ -9,7 +9,6 @@
 #include "ash/common/login_status.h"
 #include "ash/common/system/chromeos/session/logout_button_observer.h"
 #include "ash/common/system/tray/tray_background_view.h"
-#include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "ui/views/controls/button/button.h"
@@ -20,15 +19,13 @@ class LabelButton;
 
 namespace ash {
 
-class StatusAreaWidget;
-
 // Adds a logout button to the launcher's status area if enabled by the
 // kShowLogoutButtonInTray pref.
 class ASH_EXPORT LogoutButtonTray : public TrayBackgroundView,
                                     public LogoutButtonObserver,
                                     public views::ButtonListener {
  public:
-  explicit LogoutButtonTray(StatusAreaWidget* status_area_widget);
+  explicit LogoutButtonTray(WmShelf* wm_shelf);
   ~LogoutButtonTray() override;
 
   // TrayBackgroundView: